Micro-fluid ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used micro-fluid ejection head is an inkjet print head used in an ink printer. Ink jet printers continue to be improved as the technology for making their micro-fluid ejection heads continues to advance.
In the production of conventional thermal ink jet print cartridges for use in ink jet printers, one or more micro-fluid ejection heads are typically bonded to one or more chip pockets of an ejection device structure. A micro-fluid ejection head typically includes a fluid-receiving opening and fluid supply channels through which fluid travels to a plurality of bubble chambers. Each bubble chamber includes an actuator such as a resistor which, when addressed with an energy pulse, momentarily vaporizes the fluid and forms a bubble which expels a fluid droplet. The micro-fluid ejection head typically comprises an ejector chip and a nozzle plate having a plurality of discharge orifices formed therein.
A container, which may be internal with, detachable from or remotely connected to (such as by tubing) the ejection device structure, serves as a reservoir for the fluid and includes a fluid supply opening that communicates with a fluid-receiving opening of a micro-fluid ejection head for supplying ink to the bubble chambers in the micro-fluid ejection head.
During assembly of the micro-fluid ejection head to the ejection device structure, an adhesive is used to bond the ejection head to the ejection device structure. The adhesive “fixes” the micro-fluid ejection and to the ejection device structure such that its location relative to the ejection device structure is substantially immovable and does not shift during processing or use of the ejection head. The bonding and fixing step often referred to as a “die attached step.” Further, the adhesive may provide additional functions such as serving as a fluid gasket against leakage of fluid and as corrosion protection for conductive tracing. The latter function for the adhesive is referred to as apart of the adhesive's encapsulating function, thereby further defining the adhesive as an “encapsulant” to protect electrical component connections, such as a flexible circuit (e.g., a TAB circuit) attached to the micro-fluid ejection head, from corrosion.
However, the micro-fluid ejection head and the ejection device structure typically have dissimilar coefficients of thermal expansion. For example, micro-fluid ejection heads may have silicon or ceramic substrates that are bonded to an ejection device structure that may be a polymeric material such as a modified phenylene oxide. Thus, the adhesive and encapsulant must accommodate both dissimilar expansions and contractions of the micro-fluid ejection head an the ejection device structure, and the resistant to attack by the ejected fluid.
Conventional adhesive and encapsulant materials tend to be non-flexible and brittle after curing due to high temperatures required for curing and relatively high shear modulus of the adhesive materials upon curing. Such properties may cause the adhesive or encapsulant materials to chip or crack. It may also cause the components (e.g., micro-fluid ejection head and/or ejection device structure) to bow, chip, crack, or otherwise separate from one another, or to be less resilient to external forces (e.g., chips may be more prone to crack when dropped). For example, during a conventional thermal curing process, the ejection device structure typically expands before a conventional die bond adhesive and encapsulant material are fully cured. The diebond material and encapsulant material thus move with the expanding device structure, wherein the diebond material and encapsulant material cure with the device structure in an expanded state. Upon cooling the device structure, the device structure contracts and, with a rigid cured diebond material or a rigid cured encapsulant material, high stress may be induced onto the ejection head structure to cause the aforementioned bowing, chipping, cracking, separating, etc.
Such adverse effects as bowing, chipping, cracking, separating, etc., may be even more pronounced as the substrates for the device structure are made thinner. Among other problems, such events may result in fluid leakage, corrosion of electrical component, and poor adhesion as well as malfunctioning of the micro-fluid ejection heads, such as misdirected nozzles. Moreover, attempts to make adhesive materials and encapsulant materials more flexible after curing often lead to materials that are less resistant to chemical degradation by the fluids being ejected.
Accordingly, a need exists for, amongst other things, a flexible encapsulant material that is curable at relatively low temperatures and that is suitable for use in assembling micro-fluid ejection head components, and particularly, for protecting electrical connections to a substrate for a micro-fluid ejection head.
With regard to the foregoing and other object and advantages, various embodiments of the disclosure provide a thermally curable encapsulant material for a micro-fluid ejection head and methods for making a micro-fluid ejection head having increased planarity. The encapsulant material may be provided by a composition including from about 50.0 to about 95.0 percent by weight of at least one cross-linkable epoxy resin having a flexible backbone, from about 0.1 to about 20.0 percent by weight of at least one thermal curative agent, and from about 0.0 to about 50.0 percent by weight filler. Upon curing the encapsulant material exhibits a relatively low shear modulus.
Additionally, embodiments provide a method for protecting a micro-fluid ejection head. The method includes applying a thermally curable encapsulant material adjacent to a fluid ejection surface of the ejection head. The encapsulant material contains from about 50.0 to about 95.0 percent by weight of at least one cross-linkable epoxy resin having a flexible backbone, from about 0.1 to about 20.0 percent by weight of at least one thermal curative agent, and from about 0.0 to about 50.0 percent by weight filler. The encapsulant material is cured and when cured exhibits a relatively low shear modulus.
Other exemplary embodiments of the disclosure may provide a micro-fluid ejection head having a thermally curable encapsulant disposed adjacent to a fluid ejection surface thereof, wherein the encapsulant has a shear modulus of less than about 10.0 MPa at 25° C.; and/or glass transition temperature of less than about 90° C.
Advantages of the exemplary embodiments may include, but are not limited to, a reduction in ejector chip substrate bow, an increase in ejector head durability, increased planarity of the ejector head, and the like. The planarity of an ejector head is defined as the slope of each fluid ejection nozzle. Other advantages may include the provision of adhesives and encapsulant materials having improved mechanical, adhesive, and corrosion resistance properties. Reduced stresses, which may reduce ejection head fragility, may be present in the ejector head substrates due to the presence of improved encapsulant material and/or die bond adhesives according to the disclosed embodiments.